In a typical wireless communication system such as a cellular radio frequency (RF) radiotelephone system, a base station communicates with a mobile communication unit, or mobile station, operating within an area served by the base station system.
Multiple access wireless communication between the base station and the mobile station occurs via RF channels that provide paths over which communication signals such as voice, data, and video are transmitted. Base-to-mobile station communications are said to occur on a forward- or down-link channel, while mobile-to-base station communications are referred to as being on a reverse- or up-link channel.
Code division multiple access (CDMA) is one example of a well-known digital RF channelization technique. A communications system using CDMA channelization is described in detail in TIA/EIA Standard IS-2000-1 Introduction to cmda2000 Standards for Spread Spectrum Systems [IS-2000-1]; TIA/EIA Standard IS-2000-2 Physical Layer Standard for cdma2000 Spread Spectrum Systems [IS-2000-2]; TIA/EIA Standard IS-2000-3 Medium Access Control (MAC) Standard for cdma2000 Spread Spectrum Systems [IS-2000-3]; TIA/EIA Standard IS-2000-4 Signaling Link Access Control (LAC) Standard for cdma2000 Spread Spectrum Systems [IS-2000-4]; and TIA/EIA Standard IS-2000-5 Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems [IS-2000-5], Telecommunications Industry Association, Washington, D.C. IS-2000-1, IS-2000-2, IS-2000-3, IS-2000-4, and IS-2000-5 [collectively, the IS-2000 Standard] are incorporated herein by reference.
Typically, all users of a CDMA system transmit and receive communications signals over a common frequency spectrum, and specialized codes, such as Walsh codes, are used for separating multiple communication signals from one another in the system. Each specialized code typically represents one communication channel within the common frequency spectrum. A communication channel may be, among other things, a paging channel or a traffic channel.
The IS-2000 standard provides for paging channels divided into time slots, or paging channel time slots. One or more paging channels may be used by the base station. Within those paging channels, a plurality of paging channel time slots are assigned to the mobile station. A base station transmits pages and other messages to a mobile station in the paging channel time slots assigned to that mobile station.
The IS-2000 standard further provides for quick paging channels. Quick paging channels, like paging channels, are divided into time slots, or quick paging channel time slots. When a mobile station is to receive a message on a paging channel, the base station enables one or more paging indicators on the quick paging channel to alert the mobile station that it should monitor its assigned paging channel. This alleviates the requirement that a mobile station monitor every assigned time slot of the paging channel for messages. Instead, the mobile station may enter a sleep mode, waking only to monitor its assigned paging indicators on the quick paging channel. If an assigned paging indicator is enabled, the mobile station wakes up to receive a message on the paging channel. Otherwise, the mobile station may return to the sleep mode until the time of its next scheduled paging indicator. Because the paging indicators are relatively short, the mobile station conserves energy by remaining in the sleep mode for longer periods of time. Consequently, the mobile station's battery life is increased.
To increase the probability that a mobile station will determine correctly the status of a paging indicator, paging indicators, when enabled, are typically transmitted at a high power level. When a base station is required to transmit multiple paging indicators simultaneously, the peak power level of the quick paging channels can be significant. In order to allow for higher peak power levels on the quick paging channels, the base station may be forced to reduce the amount of power amplifier capacity reserved for traffic channels, thereby reducing the base station capacity. Accordingly, it may be desirable to limit the number of paging indicators simultaneously transmitted by a base station.
There is therefore a need for an improved mechanism of scheduling messages to be transmitted over a wireless communications system that reduces the quick paging channel peak power level by limiting the number of paging indicators that are transmitted simultaneously.